1. Field of the Invention
The present invention relates to a laser device and a light signal amplifying device. In particular, it relates to a laser device for laser oscillation by introducing an exciting light to a laser activating substance contained inside an optical fiber, and a light signal amplifying device using the laser device.
2. Description of the Related Art
In the field of optical communication or optical processing technology, development of an inexpensive high output laser device is called for. Conventionally, as a prospective device capable of satisfying the demand, an optical fiber laser device is known. Since the optical fiber laser device promotes the interaction between a laser activating substance and a light by containing the light with a high density as well as increases the interaction length by prolonging the length, a high quality laser beam can be generated three-dimensionally.
In such a laser device, in order to realize a high output or a high efficiency of a laser beam, the issue to be tackled is how an exciting light can be introduced efficiently to a core of an optical fiber with a laser activating substance added. However, in general, since the core diameter is limited to several ten xcexcm or less if the core is set at a single mode waveguide condition, it is difficult to introduce an exciting light efficiently to the end face of this diameter. Therefore, a laser device capable of improving the introduction efficiency of the exciting light and the light collecting property of the output laser beam by introducing the exciting light from the side surface of the optical fiber has been proposed.
For example, JP-A-10-190097 discloses a laser device comprising a structure with an optical fiber integrated by an optical medium in a dense state such that a laser beam is outputted from the end face of the optical fiber by directing an exciting light from the peripheral part of the structure. According to such a device, since the exciting light is introduced from the side surface of the optical fiber, compared with the case of introducing an exciting light from the end face, the exciting light introducing area is dramatically larger. Besides, since the laser beam to be outputted is only of the mode determined by the waveguide structure of the optical fiber, the outputted light from the optical fiber can be collected approximately to the core diameter. Therefore, in the case the fiber is for propagating only the single mode, the taken out light can be collected to the analysis limit. Accordingly, a laser beam of a far higher luminosity than that of the exciting light can be obtained.
However, according to the laser device disclosed in JP-A-10-190097, since the exciting light propagates while traversing the optical fiber, propagation attenuation and scattering loss of the exciting light should be prevented in the gaps in the optical fiber. Therefore, integration of the optical fiber by thermal fusion, and filling the gaps in the optical fiber with an organic adhesive can be conceivable.
Although the gaps can be filled relatively easily with the organic adhesive in the optical fiber, since it is an organic substance, it has a low light resistance power property, and thus the mechanical strength may not be sustained under a strong excitation of several hundred W or more, or the adhesive may be denatured so as not to maintain the transparency.
Moreover, the method of integrating the optical fiber by thermal fusion is carried out by filling the gaps in the optical fiber completely with a glass equivalent to the mother material of the optical fiber. Although the method is highly reliable, since the optical fiber should be fused at a high temperature of 1,500xc2x0 C. or higher in the case the optical fiber is made from a glass with a high melting point, such as a silica glass, the core of the optical fiber may be deformed. Moreover, a problem arises in that it is difficult to develop an auxiliary jig for keeping the shape, capable of enduring the temperature.
The present invention has been achieved for solving the above-mentioned problems, and an object thereof is to provide in an easily production step a laser device having the excellent exciting light introduction efficiency and laser oscillation efficiency, and a high resistance with respect to light and heat accompanying the laser oscillation, and a light signal amplifying device using the laser device.
In order to achieve the object, as a result of elaborate study, the present inventor has found out that an organic-inorganic hybrid material having both characteristics of an organic polymer resin with an easy handling convenience, and of an inorganic metal oxide glass with the excellent light resistance and eat resistance provides the excellent properties as an optical medium for fixing an optical fiber in a dense state so as to complete the invention.
The invention provides a laser device with an optical fiber containing a laser activating substance in the inside for emitting a laser beam from the end part in the case the laser activating substance is excited, fixed in a dense state at least partially by an optical medium, wherein the optical medium is an organic-inorganic hybrid material having a 400xc2x0 C. or lower curing temperature, and once it is cured, a 300xc2x0 C. or higher thermal decomposition starting temperature, a 1.40 to 1.56 refractive index by an exciting light wavelength capable of exciting the laser activating substance, and a transparency of a 0.5 dB/cm or less loss.
According to the invention, since the flowability of the optical medium can be lost at a 400xc2x0 C. or lower curing temperature, the laser device production can be facilitated as well as there is no risk of the optical fiber core deformation at the time of the production. Moreover, since it has a 300xc2x0 C. or higher thermal decomposition starting temperature once it is cured, the device is not damaged by heat or light accompanying the laser oscillation. Furthermore, since the optical medium has a 1.40 to 1.56 refractive index by an exciting light wavelength capable of exciting the laser activating substance, the refractive indices of the optical fiber and the optical medium can be set at the same level, and thus the scattering loss of the exciting light at the boundary of the optical medium and the clad can be restrained to a minimum level. Moreover, since it as a transparency of a 0.5 dB/cm or less loss, attenuation of the exciting light n the optical medium can be prevented. Therefore, a laser device having the excellent exciting light introduction efficiency and laser oscillation efficiency, and a high resistance with respect to light and heat accompanying the laser oscillation can be provided in an easy production step.
In the invention, as the optical medium having the properties, an organic-inorganic hybrid material including a repeating unit represented by a general formula RSiO1.5 (wherein R represents an alkyl group, a hydroxyl group, a phenyl group, a vinyl group, a 2-chloroethyl group, a 2-bromoethyl group, a hydrogen, a heavy hydrogen, a fluorine, or an oxygen. However, one having R entirely as an oxygen is excluded Moreover, R may be different per each repeating unit.), can be presented.
Specifically, as the optical medium having the properties, an oligomer or a polymer including a polymethyl silsesquioxane, a polymethyl-hydride silsesquioxane, a polyphenyl silsesquioxane, a polyphenyl-methyl siisesquioxane, a phenyl silsesquioxane-dimethyl siloxane copolymer, a polyphenyl-vinyl silsesquioxane, polycydlohexyl silsesquioxane, a polycyclopentyl silsesquioxane, a polyhydride silsesquioxane, a poly(2-chloro ethyl) silsesquioxane, a poly(2-bromo ethyl) silsesquioxane, a mixture thereof, or a mixture of them and a polysiloxane, or an amorphous silica produced by curing a poly(2-chloro ethyl) silsesquioxane, a poly(2-bromo ethyl) silsesquioxane, or a mixture thereof, or the like, can be presented